Cherts from the Middle Devonian Onondaga Formation of
the Niagara Peninsula in Southern Ontario and Western New
York State can now be distinguished from those of the Early
Devonian Bois Blanc Formation of the same area based on
differences in petrology, acritarchs, spores, and "Preservation
Ratio" values. The finely crystalline, carbonate sediments
of the Bois Blanc Formation were deposited under shallow,
low energy conditions characterised by the acritarchs Leiofusa
bacillum and L. minuta and a high relative abundance of the
spore, Apiculiretusispora minor. The medio crystalline and
bioclastic carbonate sediments of the Onondaga Formation
were deposited under shallow, high energy conditions except
for the finely crystalline lagoonal sediments of the Clarence
Member which is characterised by the acritarchs Leiofusa
navicula, L. sp. B, and L. tomaculata . The author has subdivided
and correlated the Clarence Member of the Onondaga Formation
using the "Preservation Ratio" values derived from the
palynomorphs contained in the cherts. Clarence Member cherts
were used by the Archaic people of the Niagara Peninsula
for chipped-stone tools. The source area for the chert is
considered to be the cobble beach deposits along the north
shore of Lake Erie from Port Maitland to Nanticoke